3.1. Leaching of Orange Wastes and Subsequent Digestion. In
order to select a proper solvent for limonene recovery, four
solvents including hexane, diethyl ether, dichloromethane,
and ethyl acetate were used to extract the limonene followed
by digestion of the pretreated orange peel waste for confirmation.
The pretreated orange peel waste was digested at
different concentration of volatile solids ranging from 0.5 to
2%.The results show that, for all VS concentration added, the
orange peel pretreated with hexane gave the highest methane
yield (Figure 1). Hence, the pretreatment using hexane was
further investigated in order to obtain the best pretreatment
method.
In the optimization study for pretreatment using hexane,
four factors of leaching with two levels including temperature
(20 and 40∘C), time (10 and 300min), orange peel waste
and hexane ratio (1 : 2 and 1 : 12), and the citrus waste size
(homogenized and chopped) were investigated. The pretreated
orange waste was then digested to select the best